Rankine cycle engine

ABSTRACT

A power conversion system employing an organic fluid, toluene, including a supercritical heater for vaporizing the organic feed liquid, a turbine for expanding the vapor and providing a mechanical output, a regenerator for receiving superheated vapor from the turbine and preheating a portion of the feed liquid to the main heater, and an economizer built around the main heater for preheating a portion of the feed liquid, cooling the exiting combustion gases in the economizer and directing the preheated liquid to the main heater along with feed liquid from the regenerator.

United States Patent [191 Niggemann Nov. 6, 1973 [54] RANKINE CYCLEENGINE FOREIGN PATENTS OR APPLICATIONS [751 llnvenmn fi NiggemannaRockford, 644,925 7/1962 Canada 60/107 [73] Assignee: SundstrandCorporation, Rockford, Primary Examiner-Martin Schwadro" AssistantExaminerH. Burks, Sr. Attorney-Axel A. Hofgren et al. [22] Filed: July6, 1971 [2!] Appl. No.: 159,804 [57] ABSTRACT A power conversion systememploying an organic fluid, [52] Us. CL 60/36 60/107 122/479 R toluene,including a supercritical heater for vaporizing [51] Int 170" 25/00 theorganic feed liquid, a turbine for expanding the [58] Field of Sear'ch122/479 vapor and providing a mechanical output, a regenera- 122/256 torfor receiving superheated vapor from the turbine and preheating aportion of the feed liquid to the main [56] References Cited heater, andan economizer built around the main heater for preheating a portion ofthe feed liquid, cool- UNITED STATES PATENTS ing the exiting combustiongases in the economizer and 2,160,644 5/1939 Clarkson l22/250 Rdirecting the preheated liquid to the main heater along 312 et 232 withfeed liquid from the regenerator. 3:040:528 6/1962 Tabor et al. 60/36 i2Claims, 2 Drawing Figures ECONOMIZEI? BBQ/3N6 LUB. K14 4 4 TU/Ffl/IUE CT/30L I BW/WNQ I 72 eaezz @mrevz Imam/m1? I 15 A/OM- scum/V5055 CONDEN55R smkr mm H W511 sums-74M) i i JET HE PUMP PUMP LP PUMP F ay RANKINECYCLE ENGINE BACKGROUND OF THE PRESENT INVENTION Power conversionsystems have been provided in the past that employ organic fluids as theworking fluid of the system. The use of an organic fluid in the RankineCycle has many advantages. Firstly, thepositive slope of the saturatedvapor line on the temperature entropy diagram results in dry expansion,without turbine erosion, and ability to operate at optimum speedswithout wheel stress problems. Moreover, organic fluids provide a widerange of freezing points, thermal stability, system pressure level andcost, that enable one or more fluids to be particularly useful in agiven power conversion system.

The present invention has applicability to the generation of mechanicalor electric power from thermal power. In some applications there is alow temperature start-up requirement that would render undesirable anyfluid that is frozen, slushy, or even highly viscous at the start-uptemperature. Because of the high temperature degradation with theresulting noncondensable gas production in organic fluids, it isdesirable that the organic fluid have good thermal stability. 1

Various organic fluids have been tested, and it has been found that manyhave disadvantages such as poor thermal stability, relatively highfreezing points, and relatively low back pressures.

SUMMARY OF THE INVENTION In accordance with the present invention, apower conversion system is provided employing toluene as the workingfluid. Toluene is typical of the organic working fluids in that thevapor superheats upon expansion from a high to a low pressure. Thisresults in a fairly low prime mover isentropic head and a relativelyslow turbine tip speed so that a single stage turbine can be employed atits best efficiency safely within the turbine wheel stress limits.

The major components in the system are a supercriticalheater-economizer, a single-stage turbine which may drive an alternator,a regenerator, a condenser and a feed pumprToluene is the working fluidbecause of its -1 39 FJfreezing point, its good thermal stability, itsrelatively high system pressure level which leads to compact heattransfer equipment, and its commercial availability.

The supercritical system cycle is selected so that the boiler becomes aliquid heater that precludes hydrodynamic instability, makes very highheat transfer rates possible without excessive wall temperatures, andresults in a very small fluid inventory in the heater which minimizesfluid degradation and stored energy. The heater-economizer may be acompact cylindrical unit with the burner surrounded by the heatexchanger. The

combustion gases pass over the heat absorbing surfaces of the heater,heating the mixed flows from the regenerator liquid outlet and theeconomizer liquid outlet to the vapor outlet temperature in the heater.

The combustion gases exit the heater section and are ducted through asurrounding economizer which further cools the gases, thus minimizingstack loss. About 20 percent of the feed liquid is fed to the economizerfor preheating the same and reducing the hot gas exit temperature. Theeconomizer feed liquid flow, preheated, is mixed with the other feedliquid (approximately 80 percent) of the system flow at the heaterinlet. The percent feed liquid flow passes from the feed pump outletthrough the vapor-liquid regenerator. Because of the relatively highback pressure provided in the system through the useof toluene, theregenerator is quite small even though 20 percent of feed liquidbypasses the regenerator, requiring increased heat exchange capacity inplace of unavailable liquid. The passing of 20 percent of the feed flowthrough an economizer allows a significant reduction in flue gas stackloss and a commensurate increase in plant efficiency. The high pressurehot fluid from the heater outlet passes through a suitable vapor flowcontrol device to a single stage impulse turbine. In an electrical powersystem, the turbine may be connected to drive either directly or througha gear box alternator and also a system pump. The turbine exhaust ispassed through the vapor side of the regenerator where it preheats thefeed liquid on its way to the heater. From the exit of the regenerator,the vapor is ducted to a condenser where the waste heat is rejected tothe condenser coolant. In

some applications, this waste heat can be utilized for heating and/orfor driving an adsorption air conditioner.

A device is provided for separating the noncondensable gases that arepresent in the vapor in the condenser. This device confines theconcentrated noncondensable gases in a separate container and preventsnoncondensable gas accumulation. in the condenser. If these gases wereallowed to accumulate in the condenser such that the noncondensable gaspartial pressure approached 1 percent of the total condenser pressure,the resulting reduced condensing coefficient would increase condenserpressure and reduce cycle efficiency. From the condenser the condensatedrains into a hotwell. A jet pump draws condensate from the hotwell andincreases pressure to system inlet pressure. The system pump has twooutlets providing high pressure primary flow to the system and also lowpressure flow to the jet pump. This minimizes the system pumping power.The main system flow is'directed from the impeller pump to theregenerator and to the economizer. 1

Toluene was selected as the system working fluid for several reasons. Ithas a 1 39 F. freezing temperature which makes it desirable for cold.starts. The thermal stability of toluene is greater than most organicfluids. Toluene has a high back pressure in an air cooled Rankine cyclepower system, i.e., 8 psi at 200 F. The high back pressure in a toluenesystem permits a small high speed turbine, and a low volume and lowweight regenerator, even with 20 percent of the liquid feed bypassed tothe economizer. Toluene has thermal stability capabilities attemperatures well in excess of its critical temperature which allows theuse of a compact, high heat flux, low fluid inventory supercriticalvaporizer, where low inventory subcritical vaporizers (once-throughboilers) are subject to hydrodynamic instability. The net result is aminimization of component size which is desirable from a packagingstandpoint, and a maximization of plant efficiency due to theincorporation of the economizer utilizing regenerator bypass liquid andalso due to the ability to operate at high turbine inlet temperaturewhich is allowed by the basic good thermal stability of toluene and alsobecause of the very low fluid inventory in the heater as a result of thesupercritical vaporizer.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration ofa power conversion system according to the present invention; and

FIG. 2 is a schematic illustration of a heatereconomizer according tothe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As viewed in FIG. 1, a powerconversion system is seen to include, generally, a heater-economizer 12which delivers toluene vapor to a turbine 14, with exhaust vapor fromthe turbine passing through a regenerator 15 decreasing the vaportemperature and increasing the temperature of the feed liquid to theheater-economizer 12. The vapor from the regenerator is condensed incondenser 16 and the condensate passes to hotwell 18 with thenoncondensable gases being separated by separator 20. A jet pump 22withdraws condensate from hotwell 18 and conveys the same to a pump 25which supplies feed liquid to the system. A start tank 27 is providedfor filling the system during start-up.

The jet pump 22 is provided to boost the pressure level of condensate inhotwell 18 up to a pressure which will prevent cavitation of the mainsystem condensate pump 25. Jet pump 22 delivers fluid to main systempump 25 which may be a stepped impeller pump having two outlet diffusersat different radii. The inner diffuser provides fluidthrough line 30 todrive jet pump 25 and the outer diffuser provides fluid at 710 psithrough line 31 to provide main system flow across check valve 32. Fromline 32, about 80 percent of the organic feed liquid toluene is conveyedthrough line 35 to cooling tubing 37 associated with the alternator (notshown) for cooling the stator thereof. The feed liquid exits the statorcooling device 37 in a typical system at about 212 F., since it takes upheat generated by machine losses. 1

Feed liquid at 212 F. is delivered to regenerator 15. The regenerator 15may be a plate fin heat exchanger arranged in a folded counterflowconfiguration. Since the vapor is relatively dense and the flow rate islow, the heat exchanger requires a small vapor frontal area and longlength in order to increase the heat transfer coefficient and at thesame time maintain sufficient heat transfersurface. The fins may be madeof wavy nickel metal, while separator sheets, top and bottom plates,side channels and headers are all made of stainless steel, resulting ina unit having a small volume and low weight.

Flow leaving the regenerator 15 on the liquid side through line 38 is atapproximately 488 F., in an exemplary installation. Before entering theheatereconomizer 12, the flow leaving the liquid side of the regeneratormixes at 40 with the preheated flow from economizer 42.

The economizer 42 is fed feed liquid through line 44, amounting to aboutpercent of the total system feed liquid. The heater-economizer is shownmore clearly in FIG. 2 and is a supercritical once-through unit ofcompact design. High mass velocity through the heater insures high heattransfer thereby minimizing the hot spots. The vaporizer-economizer 12includes combustion gas inlets 49 and 50 which receive combustion gases,a central combustion gas chamber 52 at about 3,000 F., for example, anannular heater section 55 and an annular economizer section 42. In theheater section 55, a brazed sphere matrix 56 is provided on the flue gasside to provide a large gas side heat transfer area. Heater tubes 60 areprovided packed with a sphere matrix 62 to increase mass velocity andheat transfer coefficient.

The economizer section 42 includes liquid feed tubes 63 surrounded by abrazed sphere matrix 55 through which the flue gases pass.

In operation of a typical system embodying the invention, the feedliquid flowing through tubes 63 reduces the flue gas temperature fromabout 800 F. exiting from heater section 55 to approximately 400 F.,thereby increasing cycle efficiency significantly. The pressure of theliquid exiting economizer 42 is equal to the pressure at the regeneratoroutlet line 38 to maintain the proper flow split (i.e., about 80percent-20 percent). This is accomplished by matching the hydraulicimpedance of economizer 42 with that of regenerator 15. The temperatureof the liquid exiting the economizer in line 68 is approximately 490 F.This flow combines at 40 with the flow from regenerator line 38 andpasses through line 70 to the heater tubes 60. Vapor leaving thesuper-critical heater section 55 exits the heater through line 72somewhat above 700 F. and over 600 psia.

The high pressure, high temperature vapor in line 72 is controlled by avalve 75 decreasing the turbine inlet pressure somewhat, e.g., to 575psia. The valve 75 is a speed responsive control for maintaining thespeed of turbine 14 constant.

A shut-down valve 78 is provided which responds upon a predeterminedtemperature in heatereconomizer 12 to open, permitting flow initiationto the turbine 14.

The turbine 14 is a single stage, supersonic, axial im pulse, partialadmission turbine. The organic working fluid toluene superheats uponexpansion enabling high pressure ratios to be taken across the singlestage of turbine 14 resulting in high cycle efficiencies. Thedeleterious effect of moisture formation in the turbine nozzles andpassages which would otherwise cause blade erosion and lack of flowcontrol is not present. The turbine 14 may, for example, run at 120,000RPM.

Vapor exiting the turbine 14 at 6.29 psia at 527 F., as indicated byline 80, is directed to the vapor side of regenerator 15. Vapor exitsthe regenerator 15 through line 82 at 6.09 psia and 243 F. This vaporenters the condenser 16 where the vapor is condensed. The condenser 16is a fin heat exchanger with the vapor condensing inside tubes and thecooling air flowing across the tubes and between the finned surfaces. Afan (not shown) is provided for directing ambient air across the tubesin condenser 16.

The degradation of toluene results in the generation of noncondensablegases and high boiling compounds. The noncondensable gas separator 20 isprovided to prevent a decrease in the condenser heat transfercoefficients and to prevent an increase in the turbine back pressurewhich would otherwise reduce turbine power and cycle efficiency.

The condensed vapor flows through line 85 into the hotwell 18.

The start-up tank 27 includes a spring loaded valve (not shown) with alocking device for initiating flow from the start tank. During start-up,the burner air and fuel equipment (not shown) would be activated aswould an igniter (not shown) delivering hot air to the heater-economizer12. Once the flame is proved, and the heater metal reaches a criticaltemperature, means are provided for releasing the locking deviceassociated with start tank 27 and allowing the spring to force highpressure liquid to fill the high pressure lines 31, 35 and 44. This alsoinitiates flow to the bearings as indicated in FIG. 1. While the heatermetal and working fluid are coming up to temperature, the loop 30 frompump 25 to pump 22 is being filled by bleeding a small amount of highpressure fluid.

When the heater temperature reaches a certain level, the shut-down valve78 is opened admitting flow to the turbine. The turbine then acceleratesto 120,000 RPM in about to seconds. When the turbine is nearly up tospeed, the system pump will put out more pressure than the start tank 27and the check valve 32 will open supplying system flow. When the turbineis up to speed, the condenser fan (not shown) is activated and batteriesassociated with the burner are recharged. When the condensate in hotwell18 reaches a temperature near its normal operating point, the unit isready to supply fullload. This occurs rapidly since the system isrelatively light and has a liquid inventory (toluene) of about 3 pounds.Start-up time can be further reduced if the alternator associated withturbine 14 is loaded in a programmed fashion to supply electric energyto heaters'wrapped around the hotwell.

After system shut-down, a battery driven motor (not shown) is activatedto reset the spring on start tank 27 to its prestart position. A crankmay also be provided to compress the start tank spring.

While the system has been shown and described in connection with theprovision of power to a turbine for driving an alternator in anelectrical power supply system, it should be understood that utility ofthe invention is not limited to electrical systems, and it may beutilized to drive a turbine to supply power to an automotive vehicletransmission, for example.

I claim: V

l. A power conversion system employing the Rankine cycle, comprising: asource of organic fluid feed liquid, a combustion gas heater for heatingthe feed liquid to a high pressure-high temperature state, a turbineconnected to receive the hot fluid from the heater, a regeneratorconnected to receive exhaust vapor from the turbine, said regeneratorbeing constructed to pass at least a portion of said feed liquid inout-of-contact heat exchange relation with vapor from said turbine, andan economizer forming. a part of the combustion gas heater for passingat least another. portion of the feed liquid in out-of-contact heatexchange relation to the combustion gases from the heater to reduce thegas exit temperature.

2 A power conversion system as defined in claim 1, wherein the organicfluid is toluene.

3. A power conversion system as defined in claim 1, including means fordirecting a minor portion of the feed liquid to the economizer, andmeans for combining the preheated feed liquid from the economizer andthe preheated feed liquid from the regenerator and directing thecombined liquid to the combustion gas heater.

4. Apower conversion system employing the Rankine cycle, comprising; asource of organic feed liquid including a first feed liquid, acombustion gas heater for the feed liquid to raise the temperature andpressure thereof, a turbine constructed to receive vapor from the heaterto drive the turbine in expansion, means for receiving and condensingthe vapor from the turbine, and an economizer associated with andforming a part .of the combustion gas heater for receiving at leastanother portion of the feed liquid in out-of-contact heat exchangerelation with the hot combustion gases exiting the heater, and means foradding feed liquid from the economizer with said first feed liquid anddirecting the combined feed liquid to the combustion gas heater.

5. A power conversion system as defined in claim 4, including aregenerator for preheating at least a portion of the feed liquid, saidregenerator receiving superheated vapor from the turbine and passing thesame in out-of-contact heat exchange relation with the feed liquid inthe regenerator.

6. A power conversion system as defined in claim 4, wherein said heateris a once through super-critical heater having a first main set ofheater tubes generally annular in configuratiommeans directing thecombustion gases outwardly across the main heater tubes.

7. A power conversion system as defined in claim 6, wherein saideconomizer includes a set of tubes surrounding the heater tubes, saidcombustion gases being directed over said preheater tubes.

8. A power conversion system as defined in claim 4, including a conduitmeans between the combustion gas heater and the turbine for conveyinghot vapor to the turbine, and a vapor flow control valve in said conduitmeans for controlling the speed of the turbine.

9. A power conversion system as defined in claim 4, including conduitmeans between the combustion gas heater and the turbine for conveyingvapor from the heater to the turbine, and a start-up valve in saidconduit means for passing vapor to the turbine when the heater reaches apredetermined temperature level.

10. A power conversion system as defined in claim 6, wherein the organicfluid is toluene.

11. A power conversion system as defined in claim 1, including means fordirecting a major portion of the feed liquid to the regenerator.

12. An organic Rankine cycle power conversion system, comprising, ahotwell for organic feed liquid, a pump for pumping'fluid from thehotwell, a regenerator for preheating feed liquid, conduit means fordirecting a major portion of the feed liquid to the regenerator, acombustion gas heater, means for conveying-feed liquid from theregenerator to the heater, an economizer forming part of the combustiongas heater including means for passing at least a portion of the feedliquid in out-of-contact heat exchange relation with exiting combustiongases to reduce the temperature of the gases, means to convey preheatedliquid from the economizer to the heater, a turbine, means for conveyingvapor from the heater to the turbine, means for conveying vapor from theturbine to the regenerator, a condenser, means for conveying vapor fromthe regenerator to the condenser, and means for conveying condensatefrom the condenser to the hotwell.

1. A power conversion system employing the Rankine cycle, comprising: asource of organic fluid feed liquid, a combustion gas heater for heatingthe feed liquid to a high pressure-high temperature state, a turbineconnected to receive the hot fluid from the heater, a regeneratorconnected to receive exhaust vapor from the turbine, said regeneratorbeing constructed to pass at least a portion of said feed liquid inout-of-contact heat exchange relation with vapor from said turbine, andan economizer forming a part of the combustion gas heater for passing atleast another portion of the feed liquid in out-of-contact heat exchangerelation to the combustion gases from the heater to reduce the gas exittemperature.
 2. A power conversion system as defined in claim 1, whereinthe organic fluid is toluene.
 3. A power conversion system as defined inclaim 1, including means for directing a minor portion of the feedliquid to the economizer, and means for combining the preheated feedliquid from the economizer and the preheated feed liquid from theregenerator and directing the combined liquid to the combustion gasheater.
 4. A power conversion system employing the Rankine cycle,comprising; a source of organic feed liquid including a first feedliquid, a combustion gas heater for the feed liquid to raise thetemperature and pressure thereof, a turbine constructed to receive vaporfrom the heater to drive the turbine in expansion, means for receivingand condensing the vapor from the turbine, and an economizer associatedwith and forming a part of the combustion gas heater for receiving atleast another portion of the feed liquid in out-of-contact heat exchangerelation with the hot combustion gases exiting the heater, and means foradding feed liquid from the economizer with said first feed liquid anddirecting the combined feed liquid to the combustion gas heater.
 5. Apower conversion system as defined in claim 4, including a regeneratorfor preheating at least a portion of the feed liquid, said regeneratorreceiving superheated vapor from the turbine and passing the same inout-of-contact heat exchange relation with the feed liquid in theregenerator.
 6. A power conversion system as defined in claim 4, whereinsaid heater is a once through super-critical heater having a first mainset of heater tubes generally annular in configuration, means directingthe combustion gases outwardly across the main heater tubes.
 7. A powerconversion system as defined in claim 6, wherein said economizerincludes a set of tubes surrounding the heater tubes, said combustiongases being directed over said preheater tubes.
 8. A power conversionsystem as defined in claim 4, including a conduit means between thecombustion gas heater and the turbine for conveying hot vapor to theturbine, and a vapor flow control valve in said conduit means forcontrolling the speed of the turbine.
 9. A power conversion system asdefined in claim 4, including conduit means between the combustion gasheater and the turbine for conveying vapor from the heater to theturbine, and a start-up valve in said conduit means for passing vapor tothe turBine when the heater reaches a predetermined temperature level.10. A power conversion system as defined in claim 6, wherein the organicfluid is toluene.
 11. A power conversion system as defined in claim 1,including means for directing a major portion of the feed liquid to theregenerator.
 12. An organic Rankine cycle power conversion system,comprising, a hotwell for organic feed liquid, a pump for pumping fluidfrom the hotwell, a regenerator for preheating feed liquid, conduitmeans for directing a major portion of the feed liquid to theregenerator, a combustion gas heater, means for conveying feed liquidfrom the regenerator to the heater, an economizer forming part of thecombustion gas heater including means for passing at least a portion ofthe feed liquid in out-of-contact heat exchange relation with exitingcombustion gases to reduce the temperature of the gases, means to conveypreheated liquid from the economizer to the heater, a turbine, means forconveying vapor from the heater to the turbine, means for conveyingvapor from the turbine to the regenerator, a condenser, means forconveying vapor from the regenerator to the condenser, and means forconveying condensate from the condenser to the hotwell.